Angle measurement systems, or angle encoder systems, are used for measuring rotary motions of a shaft across one or several rotation(s). The rotary motion is acquired either in an incremental or an absolute manner, and depending thereon, the output measured value is a sequence of counting pulses, a counter value or a code word. Angle encoder systems are used in particular in machine tools or processing centers for the measurement of rotatory motions. For example, the determination of the angle of rotation to a degree of just a few seconds of an angle is of decisive importance for rotary tables or swivel heads of machine tools, C-axes of lathes, and also for printing mechanisms of printing machines. Since extremely precise measuring results are able to be achieved when using optical measuring principles, such angle encoder systems are frequently equipped with an optical measuring system. In this case, an angle scale is often scanned using a reflected light or a transmitted light method.
In order to ensure a high measuring accuracy, it is important to protect the angle scale from contamination. It may be particularly disadvantageous if lubricant or components of such a lubricant leak(s) from the roller bearing and deposit(s) on the scanning device of the angle scale or in the region of the angle scale itself. Such contamination often takes the form of droplets and produces an optical effect similar to a lens. The light beams are deflected accordingly under these circumstances, which may lead to a faulty measurement.
European Published Patent Application No. 2 378 251 describes an angle encoder system, which has a shaft including a groove, which is connected to a hollow space for the storage of lubricants.